Electron gun structure



May 26, 1959 c. DICHTER 2,833,538

ELECTRON GUN STRUCTURE Filed April 1953 Inventor": Channin Dichter',

. b M X His Attorne g.

United States Patent 2,888,588 I "ELECTRON GUN STRUCTURE Channing Dichtel', Syracuse, 'N.Y., assignor to General Electric Company, a corporation ofNew York Application April 3, 1953, "Serial No.'346,'674

7 Claims. '(Cl. 313- 82,)

'Ihe-present'invention relatesto an improved electron gun structure :suitable for'use .in cathode ray tubes and particularly to an improved control grid structure for such tubes.

Cathode ray tubes for'use 'in television receivers are manufactured in large quantities. In the gunstructures of tubes, as currently manufactured, thegrid-to-cathode and control grid-to-acceleratinggrid spacings are rather close with the result that vmany tubes are rejected because of variations from the desired spacings which in many cases result in a .short circuit between adjacent electrodes. For commercial reasons, it is very desirable that the cutoff voltage of the electron guns of these tubes not be altered substantially from .its'present-value which is in the order of 50 volts'negative.

spot size of the'focused electron beam which is detrimental with'respect to picture'quality. The wall thickness of the grid cylinder'of the grid may'be decreased but :in constructions provided in the'past this has not been practicable.

Limitations in the "rigidity and structural stability of the grid structure has required materialhaving a thickness in the order of .008".as the absolutemin- 'imum.

In accordance with 'an "important object of the present invention, 'the'wall defining the grid aperture is of reduced thickness inth'e region immediately surrounding the aperture and is .structurally reinforced so that it remains stable as to position. In reducing the thickness of the grid member, the 'surface' thereof is also shaped to improved the shape of the electrostatic field between it and the cathode so as to improve the quality of the spot particularly as the voltage of the control grid approaches zero, that is, is made less negative to increase the intensity of the beam. The body of the grid cap is of the usual thickness to provide sufiicient rigidity for support and to Withstand the heating to which it is subjected during processing of the tube.

Further objects and advantages of the invention will become apparent as the following description proceeds, reference being had to the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing:

Fig. l is an elevational view of an electron gun structure embodying my invention;

Fig. 2 is an enlarged view in section of a portion of the gun structure of Fig. 1;

Fig. 3 is a sectional view taken along the line 33 of Fig. 2; and

Fig. 4 is an enlarged sectional view of a grid embodying a modification of my invention.

Referring now to the drawing, I have shown my invention applied to an electron gun structure including a the spacer 'collar 17.

grid-cathode assembly 1, an accelerating grid 2, a final anode 3 and an electrostatic focusing structure 4. The various electrodes which are to be insulated from one another aresupported by means of glass stalks 5 in which areembedded anumber ofstuds 6. These studs are spot welded to the various electrodes. The entire assembly is supported from the stem or header 8 bymeans of conductors connected with the lead-in conductors .9. The focusing structure 4 may to advantage bed the type described and claimed in my U.S..PatentNo. 2,732,- 511, issued January 24, 195.6, and assigned to the assignee of this application.

The grid structureembodying the present invention will be more readily-understood .by a consideration of the-enlargedsectional view of Fig. 2. The grid cathode assembly lincludes a grid cup '10 having a grid aperture :11 in the center .of the closed end thereof. The cathode o'derand a similar flange 15 welded to the cathode and engaging the oppositeside of the disk. Thedisk v13 .is .:retained withintthe cathode sleeve by means 'of a flanged ring v16 which is bonded to the .inner wall of the grid cup. .Thespacing of the cathode assembly with respect toth'e end wall of the grid cup 10 as'well as supportfor :the end of the grid cup is provided by a flangedgspacer collar or'ring member 17, having one end engaging the end wall of the grid cup and the other end resting on ithe upper 'surface'of the cathode supporting disk 13.

As stated earlier, it is an important object of the 'present invention "to provide a thinner Wall defining the grid aperture than has been practicable. As illustrated 'in the drawing, the grid wall surrounding the grid aperture'is of progressively thinner section toward the'aperture and issurrounded at some distance from the aperture by a corrugation, ridge'or rib 18 which lends'rigidity 'tothe end wall and also providesmeans forpositioning As shown in the drawing, the corrugation or rib 18 is annular and extends inwardly into'the ,grid cup 10 in the end wall or grid wall including the grid aperture 11. Additionally, "the corrugation -is of slightly larger diameter than the collar '17.

The'shape of'the outer-surface of the control member is such as to give a desired "electrostatic fieldin the gridcathode region and in the region'between the control grid and accelerating grid 2. In the preferred form of my invention illustrated, the surface of the control grid which faces the accelerating grid 2 is that of a portion of a sphere of very large diameter as compared with the diameter of the electrodes involved. As seen in Figure 2, the central portion of the end Wall of the grid cup in which the aperture 11 is located and which defines the boundary of the spherical surface or depression corresponds generally in area to the active area of the cathode.

As shown in Fig. 4, the control grid 10' may be provided with a portion 19 surrounding the aperture 11 of reduced thickness connected with the body of the grid by a straight tapered portion 20. While this slope is not quite as desirable as that shown in Fig. 2 from the standpoint of the fields produced, it is satisfactory and easier to manufacture.

While I have described a particular embodiment of my invention it will be apparent to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I aim, therefore, in the appended claims to cover all such 3 changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A control grid structure for a beam type electric discharge device comprising a diaphragm of sheet metal having a central portion with an aperture therein, the thickness of said diaphragm gradually increasing from the boundary of said aperture only to the boundary of said central portion, and an annular reinforcing rib surrounding said aperture intermediate said boundary of said central portion and the boundary of said diaphragm.

2. An electrode structure for a beam type electric discharge device comprising a cathode including an active surface, a control grid diaphragm of sheet metal supported adjacent said cathode, said diaphragm including a central portion corresponding generally in area to said active surface of said cathode and having an aperture therein, the thickness of said diaphragm being less than .005" at the boundary of said aperture and gradually increasing from said boundary of said aperture only to the boundary of said central portion, thereby to provide a depression about said aperture on the side of said diaphragm opposite said cathode, and a planar apertured accelerating electrode supported in closely spaced relation on the side of said diaphragm opposite said cathode.

3. An electrode structure for a beam type electric discharge device comprising a control grid diaphragm having an aperture therein, a cathode including an active surface, said cathode being supported on one side of said diaphragm, a planar apertured accelerating electrode supported on the opposite side of said diaphragm in closely spaced parallel relation to said diaphragm, the surface of said diaphragm on said opposite side of said diaphragm being substantially planar except for a central portion corresponding in area generally to said active surface of said cathode and surrounding said aperture, the side of said central portion facing said accelerating electrode gradually diverging with respect to the adjacent surface of said accelerating electrode to establish a desired electrostatic field pattern and provide a thinner wall at said aperture than the remainder of said diaphragm.

4. A control grid for a beam type electric discharge device comprising a cup-shaped sheet metal member having an end wall with an aperture therein and a substantially planar outer surface, a central portion surrounding said aperture the thickness of said central portion gradually decreasing from the boundary of said central portion on said outer surface of said wall toward the boundary of said aperture, and an annular reinforcing n'b struck in from the sheet metal end wall and surrounding said central portion.

5. A control grid structure comprising a sheet metal cup having a centrally located aperture in the end wall thereof, the wall surrounding the aperture being of reduced thickness as compared with the remaining wall of said cup, a transverse insulating member supported within said cup, a cathode sleeve supported from said insulating member with the end thereof positioned behind said aperture, a collar surrounding said cathode and interposed between said insulating member and said disk, an inwardly extending ridge on the end Wall of said cup surrounding said collar to reinforce said end wall and position said collar.

6. Anelectrode structure for a beam type electric discharge device comprising an apertured first electrode and an apertured second electrode including opposed substantially planar surfaces supported in closely spaced parallel relation, said second electrode including a central portion gradually decreasing in thickness from the surface of said second electrode adjacent said first electrode to the boundary of the aperture therein, and an annular reinforcing rib spaced in from the edge and surrounding said central portion of said second electrode, said rib extending away from said first electrode.

7. An electrode structure for a beam type electric discharge device comprising an apertured first electrode and an apertured second electrode including opposed substantially planar surfaces supported in closely spaced parallel relation, a central portion of said second electrode surrounding the aperture therein and facing said first electrode being dished thereby to establish a desired electrm static field pattern and to reduce the thickness of said second electrode only in the region immediately surrounding said aperture therein, and an annular rib provided in said second electrode outwardly of said central portion and extending away from said first electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,135,941 I-Iirmann Nov. 8, 1938 2,173,498 Schlesinger Sept. 19, 1939 2,391,780 Hillier Dec. 25, 1945 2,436,265 Pohle et al. Feb. 17, 1948 2,443,916 Kelar June 22, 1948 2,540,621 Johnson Feb. 6, 1951 2,581,446 Robinson Jan. 8, 1952 2,582,454 Pohle Jan. 15, 1952 2,644,906 Bondley July 7, 1953 2,666,162 Holloway et a1. Jan. 12, 1954 FOREIGN PATENTS 521,803 Great Britain May 31, 1940 iff H mmimuil 

